1. Field of the Invention
This invention relates to a slip mechanism in anchors or packers used in the oil and gas industry, and more particularly to a mechanically set retrievable packer with a torsional resistant slip mechanism. The disclosure of U.S. patent application Ser. Nos. 09/302,738, now U.S. Pat. No. 6,164,377 issued Dec. 26, 2000, and 09/302,982, now U.S. Pat. No. 6,305,474, are incorporated herein by reference.
2. Background of the Invention
It is often desirable to sidetrack or deviate from an existing well borehole for various reasons. For instance, when a well bore becomes unusable, a new bore hole may be drilled in the vicinity of the existing cased bore hole or alternatively, a new bore hole may be sidetracked from the serviceable portion of the cased well bore. Such sidetracking from a cased borehole may also be useful for developing multiple production zones. This drilling procedure can be accomplished by milling through the side of the casing with a mill that is guided by a wedge or whipstock component. It is well known in the industry that whipstocks are used to sidetrack drill bits or mills at an angle from a borehole. The borehole may be lined with pipe casing or uncased. More often than not, the previous borehole is cased.
To complete a sidetracking operation, a typical down hole assembly consists of a whipstock attached to some form of packer or anchor mechanism that holds the whipstock in place once the whipstock has been set at the desired location and angle orientation. The upper end of a whipstock comprises an inclined face. Once the whipstock is properly set and aligned, as a mill is lowered, the inclined face guides the mill laterally with respect to the casing axis. The mill travels along the face of the whipstock to mill a window and/or to create the deviated borehole.
Mechanically set anchors typically utilized to support whipstocks have one or more slips which engage the casing or borehole. Often, the holding capabilities of these conventional devices are not enough to prevent slippage or movement during sidetracking operations. It has been found that conventional whipstock supports may be susceptible to small, but not insignificant amounts of rotational movement. If a misalignment were to occur during a window milling operation, the mill could become stuck in the hole resulting in a difficult and expensive fishing operation. Another unintended result could be that a lateral well bore is drilled in the wrong direction.
Typical slip mechanisms provide minimal upward loading capability and very little torque resistant capacity. These traditional slip mechanisms use wickers or grooves machined into the outer surface of the slip to grip the well bore and resist torsional and longitudinal (axial) forces. These gripping mechanisms allowed for very limited penetration into the casing or borehole, and therefor were prone to unwanted movement. These known problems with tools in the prior art demand that drillers limit the amounts of force applied during such milling and drilling operations. This results in lower rates of penetration, and ultimately, a more costly well.
Hence, it is desired to provide an anchor and whipstock setting apparatus that effectively resists torsional forces and prevents a whipstock from rotating. It is a further desire to provide an effective whipstock support that can be run into a borehole and set using conventional wireline methods.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.